Intercontinental test of generality for spatial patterns among diverse molluscan assemblages in coralline algal turf

Abstract

The potential generality of local processes in determining spatial patterns of molluscan assemblages in turfs of Corallina officinalis is evaluated by testing hypotheses about consistency in ecological pattern on shores in Australia, Ireland and Chile. Identical sampling protocols on 2 shores in each country were used to test 2 specific hypotheses: (1) that molluscan assemblages vary significantly among patches of turf separated by tens of meters, and (2) that these assemblages differ significantly between low- and mid-shore areas. In total, 58, 24 and 27 species of molluscs were found in samples from Australia, Ireland and Chile, respectively. There was a remarkable degree of congruence in the proportion of species that were represented in broad taxonomic groups, with prosobranch gastropods accounting for 52 to 79% of the total diversity at each locality. As predicted, there was significant variation in diversity and abundance of molluscs among patches of turf separated by tens of meters on each of the shores sampled. There was, however, little consistency in the structure of molluscan assemblages at different tidal heights, with significant differences on Australian shores, weak differences on Irish shores and no clear pattern on Chilean shores. Moreover, while the richness of species and abundance of prosobranchs was significantly greater in low-shore areas in Australia and Chile, the opposite trend was found in Ireland. Overall, the results show the potential for generality of factors that have previously been demonstrated to cause patchiness in molluscan assemblages in coralline turf at scales of tens of meters. It is proposed that testing for consistency in ecological patterns can be a useful and cost-effective first step in establishing the general importance of ecological processes.